1. Technical Field
The present disclosure relates to a content management system, and in particular to technology of controlling the use of contents by terminal devices.
2. Background of the Related Art
Digital contents such as movies, music, games and digital books are at risk of being copied and used without authorization, because it is easy to copy the data of digital contents. In order to prevent unauthorized copy and use of contents (hereinafter simply referred to as “unauthorized use”), it is necessary to take measure for copyright protection.
One example of copyright protection standards applicable to contents is the Advanced Access Content System (AACS). AACS is copyright protection standards adopted for Blu-ray Discs (BD)™ (c.f. Non-Patent Literature 1).
Under the AACS, a key issuing device issues a device key for a terminal device. Using the device key, the terminal device obtains a title key for decrypting an encrypted content. Also, under the AACS, whether the device key for the terminal device is invalid or not is determined based on a Media Key Block (MKB) which is regularly issued and which contains information defining invalid device keys that have been leaked. A terminal device whose device key is determined invalid is controlled so as not to be able to acquire a title key. A terminal device that cannot acquire a title key cannot encrypt the content, and is therefore prevented from playing back the content.